The (1,0) vibrational band of the [13.10] Ω=1 – X ³Σ⁻(0⁺) transition of tungsten sulfide (WS) has been measured in absorption using Intracavity Laser Spectroscopy with Fourier transform detection (ILS-FTS). WS was synthesized in a 0.05-0.15 A DC current plasma discharge within a tungsten lined hollow cathode at 625 mTorr with 65% Ar, 17.5% He, 17.5% H₂, and a trace amount of CS₂. The spectrum was calibrated using literature values for argon lines and PGOPHER’s calibration feature [C.M. Western, J. Quant. Spectrosc. Radiat. Transfer 2016 (186), 221-242]. Three rotational branches (P , Q-, and R-branch) with four WS isotopologues (¹⁸²WS, ¹⁸³WS, ¹⁸⁴WS, and ¹⁸⁶WS) were observed in the spectrum. Molecular constants for these isotopologues were determined for both electronic states. The line positions of the (0,0) band of this transition [L.F. Tsang et al., J. Mol. Spectrosc. 2019 (359), 31-36] were included in the fit. The results of the analysis will be presented, and compared with calculations [L.F. Tsang et al., 2019].

A new electronic transition of PtF has been recorded at high resolution using Intracavity Laser Spectroscopy (ILS). The PtF molecules were produced in a current regulated RF discharge operating with 0.20-0.80 A applied to a Pt-lined Cu hollow cathode in 0.50-1.25 Torr total pressure comprised of 1-5% SF₆ in an Ar/He sputter gas mixture. This hollow cathode was located within the resonator cavity of a tunable DCM dye laser operating over the 14,500-16,500 cm⁻¹ range, and effective pathlengths of 0.4-2.0 km were utilized with the ILS method. The band system observed corresponds to the (0,0) band of the [15.3]Ω=3/2 – X ²Π_3/2 transition. Rotational assignments for the transitions have been confirmed through combination difference analysis using known ground state constants. The data were fit using PGOPHER with a standard Hund’s case (c) energy level expression. Spectra and results of the analysis will be presented.

Using ILS-FTS, we have recorded the A Ω=1 – X Ω=0⁺ transition of diatomic PtS. Strong bands were observed at 15,520 and 15,910 cm⁻¹, which have been identified as the (0,0) and (1,0) vibrational bands. The P- and R-branches show a regular pattern for the ¹⁹⁴PtS, ¹⁹⁵PtS, ¹⁹⁶PtS and ¹⁹⁸PtS isotopologues, but quite interestingly the Q-branch shows significant hyperfine splitting for ¹⁹⁵PtS. Although P- and R-branches were easily assigned based on the known ground state constants, the Q-branch seems to be perturbed, requiring q, q_D, and q_H parameters to achieve only a sub-par fit. This indicates the presence of a nearby Ω=0⁻ state that is perturbing the f–levels in the A Ω=1 state. A successful deperturbation analysis and fit were performed in PGOPHER, and molecular constants for the A Ω=1 and perturbing Ω=0⁻ states were obtained. High-level ab initio calculations support this assignment and predict an Ω=0⁻ state in close proximity to the A state. Results and discussion of this analysis will be presented.

The visible electronic transitions of the simple asymmetric top molecules CaSH and CaNH2 have been extensively studied both field-free Z. Morbi, C. Zhao, J.W. Hepburn, and P.F. Bernath, J. Chem. Phys. 108, 8891 (1998)., Z. Morbi, C. Zhao, and P.F. Bernath, J. Chem. Phys. 106, 4860 (1997)., P.M. Sheridan, M.J. Dick, J.−G. Wang, and P.F. Bernath, Mol. Phys. 105, 569 (2007). and in the presence of static electric field C.T. Scurlock, T. Henderson, S. Bosely, K.Y. Jung, and T.C. Steimle, J. Chem. Phys. 100, (1994)., A.J. Marr, M. Tanimoto, D. Goodridge, and T.C. Steimle, J. Chem. Phys. 103, (1995).. The diagonal Franck Condon factors for these metal−centered transitions make these molecules appealing for optical cycling studies^f. These molecules can be readily aligned in the laboratory frame with the application of relatively small static electric field because of their small asymmetry splitting, and relatively large permanent a− and b−components of the electric dipole moments making them attractive as venues for quantum simulation and for investigation of fundamental physics (e.g. parity non−conservation). Here we report on the analysis of the dispersed laser induced fluorescence spectrum induced by both high−resolution and medium resolution laser excitation of the A−X, B−X and C−X bands of CaNH₂ and the B−X and C−X transitions of CaSH. The experimentally determined branching ratios are compared to those predicted based on high−level electronic−structure calculations of potential energy surfaces. The molecules were generated via laser ablation/supersonic expansion and the 2D spectra (excitation vs Z. Morbi, C. Zhao, and P.F. Bernath, J. Chem. Phys. 106, 4860 (1997).C.T. Scurlock, T. Henderson, S. Bosely, K.Y. Jung, and T.C. Steimle, J. Chem. Phys. 100, (1994).

We report here on the high resolution ( ∼ 30 MHz FWHM) laser induced fluorescence spectrum of an electronic transition of YbOH observed in the 18500 - 18600 cm⁻¹region. The YbOH was produced in a supercooled molecular beam by the reaction of laser ablated Yb with methanol. Because of the large number of Yb isotopes, the rotational structure, though well resolved, was very dense. The rotational structure of three of the isotopologues, ¹⁷²YbOH, ¹⁷⁴YbOH and ¹⁷⁶YbOH was identified and assigned. The rotational analysis showed that the transition was from an excited Ω = 3/2 state, labelled [18.6]1.5, to the ground X²Σ⁺ state and having an origin of 18577.5 cm⁻¹. In order to try and determine the nature of the Ω = 3/2 state (possibly A²Π_3/2?), external magnetic fields were applied and the resulting Zeeman spectra assigned and analyzed. The previous analysisT.C. Melville and J.A. Coxon, J. Chem. Phys. 115, 6974 (2001)f a high temperature source assigned a state near 18677 cm⁻¹as A²Π_3/2. The results of the analysis will be presented and their interpretation discussed.

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Footnotes:

T.C. Melville and J.A. Coxon, J. Chem. Phys. 115, 6974 (2001)o

A direct potential fit to Hund's case (a) potential curves for the low-lying `supermultiplet' states (X²∆, ²Π, ²Σ⁺) of NiH and to R-dependent spin-orbit and rotational coupling functions has reproduced the experimental term values of ⁵⁸NiH, ⁶⁰NiH, ⁶²NiH up to 6500 cm⁻¹, with a root mean square deviation very close to the estimated uncertainty of 0.01 cm⁻¹. Second-order Born-Oppenheimer breakdown corrections to the rotational Hamiltonian had to be included to achieve this result. The spin-orbit interaction A_so(R) associated with Ni⁺ is large compared to the energy separations between the three electronic states, so that most of the observed rovibrational states are strong mixtures of the Ω-components of the multiplet. This made the fitting procedure particularly difficult, because there were no perturbation-free data to determine the starting values for the model functions. Potential curves were optimized from RKR turning-points generated from earlier work using an effective Hamiltonian approachM. Abbasi et al, J. Mol. Spectrosc. 349 49-59 (2018) and the spin-orbit and rotational coupling functions from theoretical predictionsC. Marian, J. Chem. Phys., 93(2) 1176-1186 (1990) We believe that this model may be reliably extrapolated to higher rotational states, with potential applications in the simulation of high temperature spectra, for example in the context of stellar atmospheres. M. Abbasi et al, J. Mol. Spectrosc. 349 49-59 (2018), C. Marian, J. Chem. Phys., 93(2) 1176-1186 (1990).

Beryllium is known to be a challenging test for even high level ab initio methods due to high electron correlation contributions. There is fundamental interest in understanding how well computational methods can predict physical properties of beryllium containing molecules, but very little available experimental data on these molecules. We have continued in our exploration of beryllium molecules, and have acquired preliminary spectra for the beryllium tetramer, Be₄. In this talk we will present our work to date on Be₄⁻, with comparisons to high level theory and the beryllium dimer.

We observed rotationally resolved excitation spectra of PbO for transitions from the X(0⁺) v"=0 vibronic ground state in a wavelength range of 400−450 nm. PbO molecules were produced by laser ablation in a cold helium buffer gas. The cold environment was useful to resolve overlapping rotational bands of different vibronic states. Absolute transition frequencies were measured with the uncertainty of about 10 MHz by using an ultralow expansion etalon for the laser frequency calibration. Since the previous work [1], we have continued the measurement and have observed about 1000 lines so far. The transitions to the B(1) (v′=2−6), A(0⁺) (v′=6−8), and C(0⁺) (v′=0) states were clearly assigned, and spectroscopic constants were determined precisely for three isotopic molecules ²⁰⁶PbO, ²⁰⁷PbO, and ²⁰⁸PbO. We analyzed perturbation of the B(1) levels due to the spin-orbit interaction with other Ω = 1 levels. In this talk, we will present these results and analyses, including the latest data.   [1] K. Enomoto, A. Fuwa, N. Hizawa, Y. Moriwaki, and K. Kobayashi, J. Mol. Spectrosc., 339, 12 (2017).

Laser-induced plasma is widely used as an emission source for laboratory simulations of different objects. The properties of laser plasma vary significantly depending on the pressure and composition of the environment, as well as during the evolution of the plasma plume. This property combined with the typical range of electron temperature (from 0.2 to 4 eV) and electron number density (10¹⁵ - 10¹⁹ cm⁻¹) make it a promising object for study of radiation from various plasma sources in atmosphere (combustion of meteors, airglow) and in outer space. The aim of the present work was to study structure and evolution of CaO and FeO bands in laser plasma under low pressure (0.16 to 32 Torr) that corresponds to the known spectra of Bene\checksov bolide. We obtained emission spectra of laser plasma under different pressures and observation times while ablating samples of Fe₃O₄, CaCO₃ and chondrite. In each case plasma temperature was calculated by Boltzmann plot method using 20 to 30 atomic lines. We also estimated electron number density by Saha-Boltzmann equation where possible. Study of spatial distribution of emitting atoms and molecules in plasma with precise plasma diagnostics allows to make conclusions about existence or absence of the local thermodynamic equilibrium. The obtained data show that the formation of FeO in plasma occurs with involvement of oxygen from the ablated material, but not from the surrounding atmosphere. On the contrary, CaO if formed primarily using oxygen from atmosphere. Therefore, abundance and of FeO and intensity of its emission in space objects may not depend on the pressure of the surrounding media, while CaO should have a strong dependency.

Recent observations of a possible SH absorption feature in the atmosphere of a hot Jupiter exoplanet have sparked a renewed interest in the molecule's electronic spectroscopy, motivating the creation of a new line list.Gorman et al., Mon. Not. R. Astron. Soc. 490, 1652 (2019)his list currently relies on absolute transition frequencies measured nearly 70 years ago with a grating spectrograph.Ramsay, J. Chem. Phys. 20, 1920 (1952)hile the 0.03 cm⁻¹ accuracy achieved in these experiments was impressive for the time, measurements using modern laser spectroscopy techniques can do much better. In this talk, I will present our measurements of the A ²Σ⁺,v′=0 ← X ²Π_3/2,v"=0,J"=3/2 transitions in SH using a continuous-wave ultraviolet laser stabilized to an optical frequency comb. The same apparatus was previously used to measure A−X transitions in OHFast et al. Phys. Rev. A 98, 052511 (2018) Due to the broader linewidths and lower fluorescence detection efficiency caused by a short A state predissociation lifetime, the SH transition frequencies could not be determined as precisely as those in OH. We were nevertheless able to determine the frequencies of 12 transitions from the rotational ground state with an absolute uncertainty of less than 1.2 MHz (4×10⁻⁵ cm⁻¹).

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Footnotes:

Gorman et al., Mon. Not. R. Astron. Soc. 490, 1652 (2019)T Ramsay, J. Chem. Phys. 20, 1920 (1952)W Fast et al. Phys. Rev. A 98, 052511 (2018).

Accurate and comprehensive diatomic molecular spectroscopic data have long been crucial for measuring and monitoring gaseous environments, e.g. astrophysically, as well as for benchmarking theoretical approaches and, increasingly in ultracold physics. Theory and experiment can be used independently or together to produce useful data that can be highly detailed (e.g. line lists) or summative (e.g. molecular constants). Accessing these data can be challenging; when data is compiled, knowing the right database can be sufficient, but in many cases data is not compiled or is severely out of data and manual literature searching and data extraction is thus required. Here, I will summarise my recent review of diatomic spectroscopic data (WIREs Comput Mol Sci. 2021;E1520). I will summarise the key diatomic data types and their interconnectivity. I will also provide strategies to strengthen the connection between data producers (e.g. ab-initio electronic structure theorists and experimental spectroscopists), data modellers (e.g. line list creators) and data users (astronomers, chemical physicists, etc). A particular focus is ensuring that new data is optimally utilised with appropriate attribution.

We have produced a new line list for SiO covering IR, visible and UV regions by extending the ExoMol EBJT line list for SiO to include the A ¹Π and E ¹Σ⁺ electronic states. The line list was computed using empirical potential energy curves of the states A and E refined by fitting to 2168 experimentally derived energy levels of SiO determined from 38 vibronic bands from the X-X, E-X and A-X systems states through the MARVEL procedure. The transitions dipole moments for E-X and A-X were computed with ab initio methods at the MRCI level. The line list is suitable for temperatures up to 10000 K and for wavelengths up to 150 nm. We have run the SiO line list as a Hackthon project. It was carried out internationally across different time zones. The team was composed of subgroups responsible for different tasks: the MARVEL procedure, literature review, ab initio calculations, rovibrational calculations, spectrum simulations, etc. We believe it was a successful networking event during the COVID-19 pandemic time which facilitate a collaboration in the absence of travel.

Ruthenium monoxide (RuO) molecules have been studied by laser-induced fluorescence in the UNB laser-ablation molecular-jet apparatus. Spectra with line widths of  ∼ 115MHz have been obtained allowing the seven different isotopologues of ⁿRuO (n=104, 102, 101, 100, 99, 98, and 96) to be observed. In addition, hyperfine structure due to the nuclear spin I=5/2 for the odd isotopes of ruthenium has been resolved. The 2-0, 1-0, and 0-0 bands of the [18.1]4 - X⁵∆₄ have been analyzed and the results will be compared to the earlier work of Cheung et al.N. Wang, Y.W. Ng, and A.S.-C. Cheung, J. Phys. Chem. A 2013, 117, 13279-13283.tudies of the red [16.0]5 - X⁵∆₄ transition are continuing and will also be presented.

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Footnotes:

N. Wang, Y.W. Ng, and A.S.-C. Cheung, J. Phys. Chem. A 2013, 117, 13279-13283.S

A comparative experimental and theoretical EPR study of HCO and DCO radicals, stabilized in solid CO at the liquid helium temperatures, revealed the crucial role the radical inter- and intra-molecular motions play in the spin-Hamiltonian parameters and spectral line-shapes. The HCO and, especially, DCO spectra of the highest resolution made possible thorough comparison between the experimental results and theoretical EPR spectra obtained using a variety theoretical methods. The effect from vibrational, rotational, and librational motion observed in the molecular states of formyl as a probe under low-temperature CO matrix isolation condition was obtained by motional averaging and revealed the clear proton isotope effect in the spectrum shape anisotropy using both classical and quantum approaches. As the rovibrational/librational averaging of the EPR magnetic parameters of formyl is not incorporated in standard quantum chemistry calculations, a significantly smaller Fermi contact interaction is obtained for the lighter hydrogen nucleus in the HCO isotopomer compared to experimental values in solid CO matrix at cryogenic temperatures. However, no measurable effect of this kind was detected for the deuterated DCO formyl under identical considerations. This isotope effect is discernible by the disagreement of the theoretical gyromagnetic ratios of the H/D nuclei in the quantum mechanical computations of the Fermi contact interaction.